Modified non-polluting liquid phase shale swelling inhibition drilling fluid and method of using same

ABSTRACT

The present invention provides a modified liquid phase drilling fluid having desirable properties of shale swelling inhibition, lubrication, and high temperature performance. The fluid is comprised of the following: (1) a liquid phase containing: (a) a water phase comprising fresh water, seawater, brine, simulated brine, or mixtures thereof; and (b) a water-soluble component selected from the class consisting of polyhydric alcohols, glycol, glycol ethers, polypropylene glycols, polyethylene glycols, ethylene oxide-propylene oxide copolymers (&#34;EO-PO&#34;), alcohol-initiated EO-PO copolymers and/or mixtures thereof, the ratio of said water-soluble component in the total liquid phase being from about 5% to about 50% by volume; (2) a viscosifier for suspension of solids in said liquid phase; and (3) a filtration control agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to drilling fluids used in the drilling ofsubterranean oil and gas wells. In particular, the invention provides awater-soluble synthetic component which provides lubricity and shaleinhibiting properties comparable to those of an oil-based drilling fluidwithout the adverse effects thereof.

2. Brief Description of the Prior Art

A rotary system is the most common form of drilling a subterranean well.This system depends upon the rotation of a column of drill pipe to thebottom of which is attached a multi-pronged drilling bit. The drill bitcuts into the earth, causing the cuttings to accumulate as drillingcontinues. As a result, a drilling fluid must be used to carry thesecuttings to the surface for removal, thus allowing the bit to continuefunctioning, and the bottom of the hole to be kept clean and free ofcuttings at all times

Although aqueous-based drilling fluids which utilize clear water, brine,or sea water as the primary liquid phase may be found to be dominantwithin some facets of the drilling industry, drilling fluids have beendeveloped and commercialized utilizing a hydrocarbon liquid as the majorliquid constituent. The use of such a hydrocarbon based fluid orwater-in-oil emulsion fluid is quite common in which the drilling fluidis utilized in the higher temperature wells which are drilled to themore substantial depths. These hydrocarbon fluids are referred to as oilbased fluids and normally exhibit very desirable fluid flowcharacteristics within their respective temperature utilization ranges.Additionally, such fluids are recognized as having enhanced lubricitycharacteristics, for the purpose of lubricating the drilling bit andpreventing differential sticking of the drill pipe. In addition, some ofsuch fluids have exhibited considerable beneficial shale stabilizationproperties to prevent erosion of shale or clayey substances in the wellwhich soften on hydration when exposed to an aqueous fluid formulation.Such hydrocarbon based fluids are known also to exhibit excellentfiltration properties by incorporation of a filtration control agentinto the composition to inhibit filtrate loss to the formation aroundthe bore hole.

While such hydrocarbon based fluids have been widely accepted in theindustry and have considerable advantages, such fluids also havedisadvantages, including environmental pollution effects resulting from,for example, the hydrocarbon fluid being accidentally discharged intothe sea or ocean when used on offshore wells. There is also somedifficulty in preparation at offshore locations where the barging ofconsiderable quantities of hydrocarbon based fluids is cumbersome andcomparatively expensive. Currently all oil-based fluids used offsoreU.S.A. and cuttings contaminated with oil-base fluid must be containedand hauled back to shore. This is, obviously, an expensive operation.

Shale stabilization in a fluid suspension is believed to at leastpartially be dependent upon inhibition of swelling and dispersion of theshale into the fluid. By "shales" and "shale" is meant to refer tomaterials such as bentonite and the like, claystones and "gumbo" -typecolloidal-clay substances and related substances which possess theproperty of hydrody namic volume increase when exposed to aqueousenvironments. Of particular importance is the recent geological sedimentreferred to as "gumbo" encountered in the drilling of some subterraneanwells. This "gumbo" contains a high percentage of smectite, hydrates inwater rather rapidly, becomes soft and deformable, and may swell to manytimes its original size. By "swelling" we mean to refer to thehydrodynamic volume increase of the shale. By "inhibit", "inhibition"and "inhibition of swelling" we mean the ability of a process to retardthe hydration of shales whereby they remain intact and basically intheir original size, shape and volume, said process being thepreparation of an inhibitive fluid suspension and introducing the drillcuttings generated by the drill bit into the drilling fluid suspensionas it is circulated through and out of the well.

Swelling of shales is believed to be attributable to at least twomechanisms: crystalline and osmotic. Crystalline swelling also known assurface hydration results from the adsorption of mono-molecular layersof water onto the shale surfaces. Shales usually contain a mineralcomponent which has an expandable layer-type structure which allowswater to be adsorbed on these inter-layer surfaces thus causingadditional swelling of the shale. Osmotic swelling occurs if the cationconcentration on the surfaces of the shale is greater than that in thesurrounding fluid. This difference draws the water phase between thelayers whereby ion hydration and water adsorption occurs causing anincrease in the hydrodynamic volume.

For swelling to occur by either of the aforementioned processes, theshale must interact with the water taking and/or sharing hydroxyl groupsof the water with it. In present drilling operations, shale inhibitionis achieved by addition of divalent cations or potassium ions throughbase exchange or by the addition of encapsulating and bridging polymersto the water-based fluids or, by the use of water-in-oil emulsion fluids(oil based fluids).

We have discovered a drilling fluid which provides beneficial shale andborehole stabilization without the addition of salts and/or polymers orthe use of the water-in-oil emulsion fluids. With this fluid, thereactivity of the shale is partially satisfied by a hydroxyl-bearingwater-soluble synthetic component in the fluid phase. The preferentialadsorption of these water-soluble additives fulfills the surfacereactivity requirements of the shale without the formation of bondsbetween particles and reduces the adsorption of the multi-layers ofwater which can cause swelling.

The fluid is comprised of the following: (1) a liquid phase containing(a) a water phase comprising fresh water, seawater, brine, simulatedbrine, or mixtures thereof; and (b) a water-soluble component selectedfrom the class consisting of polyhydric alcohols, glycol, glycol ethers,polypropylene glycols, polyethylene glycols, ethylene oxide-propyleneoxide copolymers ("EO-PO"), alcohol-initiated EO-PO copolymers and/ormixtures thereof, the ratio of said water-soluble component in the totalliquid phase being from about 5% to about 50% by volume; (2) aviscosifier for suspension of solids in said aqueous phase; and (3) afiltration control agent. The fluid with the water soluble componentwill exhibit a lubricity coefficient lower than that for substantiallythe same fluid without the water soluble component as determined by theAmerican Petroleum Institute's "Procedure for Determination of LubricityCoefficient (Tentative)" (1980), and the linear swelling on areconstituted "gumbo" shale inserted for about 60 minutes in saiddrilling fluid being lower than that for substantially the same fluidwithout the water soluble component, as measured by the "Swelling Test","Rigsite Shale Evaluation Techniques for Control of Shale-relatedWellbore Instability Problems", SPE/IADC Paper No. 16054, pages 52-53,(1987).

While particular water soluble synthetic additives have been used in thepetroleum industry in the past, their use as a fluid phase componentwhich enhances the lubricating and shale inhibiting characteristics of adrilling fluid has not been appreciated by those skilled in the art.Typical of such prior art is U.S. Pat. No. 4,498,994, which teaches theuse of several polyhydric alcohols or other materials as a solvent forsalt, such as calcium bromide brine, in a solids free completion fluidand method. Chemicals such as polypropylene glycols are used asindustrial lubricants and hydraulic fluids in other industries.

The present invention comprises a drilling fluid having a liquid phasewhich imparts lubricity and shale swelling inhibition properties to thefluid similar to the beneficial properties of oil-based drilling fluidswithout the accompanying adverse effects, such as high toxicity and thelike.

SUMMARY OF THE INVENTION

The present invention provides a two component liquid phase water baseddrilling fluid comprising: (1) a liquid phase containing (a) a waterphase comprising fresh water, seawater, brine, simulated brine, ormixtures thereof; and (b) a water-soluble alcohols, glycol, glycolethers, polypropylene glycols, polyethylene glycols, ethyleneoxide-propylene oxide copolymers, alcohol-initiated EO-PO copolymersand/or mixtures thereof, the ratio of said water-soluble component inthe total liquid phase being from about 5% to about 50% by volume; (2) aviscosifier for suspension of solids in said aqueous phase; and (3) afiltration control agent. The fluid with the water soluble componentwill exhibit a lubricity coefficient lower than that for substantiallythe same fluid without the water soluble component as determined by theAmerican Petroleum Institute's "Procedure for Determination of LubricityCoefficient (Tentative)" (1980), and the linear swelling on areconstituted "gumbo" shale inserted for about 60 minutes in saiddrilling fluid being lower than that for substantially the same fluidwithout the water soluble component, as measured by the "Swelling Test","Rigsite Shale Evaluation Techniques for Control of Shale-relatedWellbore Instability Problems", SPE/IADC Paper No. 16054, pages 52-53,(1987).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention comprises a two component liquid phase drillingfluid and method of using same wherein beneficial physical properties ofa hydrocarbon based drilling fluid are provided without the accompanyingadverse effects, such as high toxicity and the like.

The drilling fluid of the present invention incorporates a syntheticwater-soluble component into the liquid phase. Said component may beselected from a class of polyhydric alcohols, glycols, glycol ethers,polypropylene glycols, polyethylene glycols, EO-PO copolymers, alcoholinitiated EO-PO copolymers and/or mixtures thereof, in a percentage frombetween about 5% by volume to about 50% by volume based upon the liquidphase of the drilling fluid.

The modified liquid phase drilling fluid may comprise fresh or tap wateror brines. In the case of waters containing mono and polyvalent saltions, the drilling fluid system incorporating the present inventionshould not be salt sensitive.

The drilling fluid system of the present invention may contain knownclayey constituents forming a colloidal solids phase, such asattapulgite, sepiolite, bentonite or other compositions of clays andminerals. Typically, the drilling fluid composition of the presentinvention will incorporate from between about 0.0% by volume and about5.0% by volume of solids particulate matter hereinafter referred to as"clayey based".

Any known deflocculant may be utilized in the drilling fluid compositionof the present invention such as lignin derivatives, lignite-containingmaterials, acrylic-derived polymers and copolymers, and the like.Sodium/chrome lignosulfonates are preferably incorporated. Such aproduct is available under the trademark UNI-CAL®, trademark of andmarketed by Milpark Drilling Fluids of Houston, Tex. Typically, suchmaterial may be present in the total drilling fluid composition in anamount of from between about 0.5 pounds per U.S. 42 gallon barrel andabout 15 pounds per U.S. 42 gallon barrel.

The drilling fluid may also contain well known weighting agents, such asbarite or hematite, in any preferred amount up to a mud weight of about18 pounds per gallon.

Chemicals for use as filtration control additives which are well knownto those skilled in the art may be added also to the drilling fluidcomposition of the present invention to lower filtration rate, althoughit has been found that the drilling fluid composition of the presentinvention itself will provide some benefit as a filtration rate controlmaterial without the presence of other additives for that purpose.

Of the synthetic water soluble components defined above, tripropyleneglycol bottoms are preferred in an amount of about 30% by volume of theliquid phase of the drilling fluid composition. Tripropylene glycolbottoms is readily available from many chemical manufacturers.Compositions of these bottoms may vary from manufacturer tomanufacturer, but typical of one such bottoms is the followingcomposition: 5-20% by volume tripropylene glycol, the remainder beingpolypropylene glycol highers.

The two component modified liquid phase drilling fluid of the presentinvention has been found to have excellent lubricity characteristics.For purposes of determining lubricity, we have utilized in our testingthe "Procedure for Determination of Lubricity Coefficient" (Tentative),a standardized testing procedure published by the American PetroleumInstitute, (1980) as follows:

1. Calibration of Instrument

a. Prepare a calibration curve for conversion of ammeter reading tolubricity coefficient by using a Prony brake and procedure provided withthe instrument.

b. Recalibrate if the drive motor is altered or replaced.

2. Standardization of Test Ring and Block

a. Wash the test ring and block with water and a household cleanser.Rince thoroughly with water.

b. Place the test ring on the tapered shoulder at the bottom of theshaft and secure with the lock nut.

c. Place the test block in the holder, concave side face out, and alignwith the test ring

d. Fill the sample container with water (approximately 300 cm³) andposition it so that the test surfaces are covered.

e. Attach a rheostat in series with the instrument and turn on the drivemotor. Adjust the rheostat until the tachometer on the drive shaft reads60 rpm.

f. Apply 150 in.-lb load with the torque arm. Maintain speed at 60 rpm.

g. Observe meter reading in amperes and refer to the calibration chartfor the lubricity coefficient. Run for several minutes or until thereading stabilizes. The lubricity coefficient for water should bebetween 0.33 and 0.36. If it is not in this range, the ring and blocksurfaces should be reconditioned using one of the following methods:

(1) Continue to operate the instrument at a constant load of 150 in.-lbwith water in contact with the test surfaces. The ammeter reading shouldslowly approach the test range of 33 to 36 and then remain steady.

(2) Operate the instrument using a slurry of about 25 lb per bbl ofbentonite in fresh water and a load of 150 in.-lb. Repeat step (1).

(3) Place a grinding compound on the contact surfaces and operate theinstrument at a load of 150 in.-lb. Repeat set (1).

3. Determination of Mud Lubricity Coefficient

a. Assemble the instrument and standardize the test ring and block togive a 0.33 to 0.36 lubricity coefficient for water.

b. Stir the mud sample ten minutes on a Multimixer prior to testing.

c. Place the mud sample in the container and position to cover the ringand block.

d. Start the motor and adjust the rheostat to give 60 rpm with a load of150 in.-lb.

e. Operate the instrument until the ammeter reading stabilizes.

f. Use the calibration curve to convert the ammeter reading to lubricitycoefficient.

Shale swelling inhibition may be measured utilizing the procedureidentified on pages 52-53, "Swelling Test" of paper entitled "RigsiteShale Evaluation Techniques for Control of Shale-related WellboreInstability Problems", SPE/IADC Paper No. 16054 (1987). In addition, apenetrometer may be used to determine the hardness (or lack thereof) ofa shale sample exposed to a fluid. In this test, the depth that a needlebearing a known load penetrates the specimen is measured. The depth ofpenetration decreases as the swelling of the shale is decreased and maybe referred to as "relative hardness".

EXAMPLE I

Tests were performed and results were evaluated in order to determinethe fluid flow characteristics, lubricity parameters and shalestabilization properties of the two component modified liquid phasedrilling fluid of the present invention. A base system containing onlyfresh water and 12 pounds per barrel of pre-hydrated bentonite wasprepared and compared to three suspensions containing 12 pounds perbarrel of a prehydrated bentonite and fresh water which contained 10, 20and 40 % by volume, respectively, of neutralized tripropylene glycolbottoms (TPGB). Rheological properties were taken after "hot rolling" at150° F. for 16 hours. Plastic viscosity, yield point, initial gel and 10minute gel readings were determined using standard API testingprocedures. To one of the samples (Sample "C"), was added 0.3 pounds perbarrel of lignosulfonate deflocculant, in order to prepare the samplesfor evaluation. The results of this test, in Table 1, below, show thatpreparation of the two component modified liquid phase drilling fluid ofthe present composition incorporating a polypropylene glycol mixturewill not adversely effect rheological properties when compared to asimilar base fluid. All of the measurements set forth in Table 1 arewithin acceptable parameters.

                  TABLE 1                                                         ______________________________________                                                          Sample No.                                                  Composition, lb/bbl*                                                                          Base    A       B     C                                       ______________________________________                                        Bentonite       12      12      12     12                                     TPGB (neutralized)                                                                             0      34.8    69.7  139.3                                   (TPGB, % Vol of  0      10      20     40                                     liquid phase)                                                                 Lignosulfonate  --      --      --     0.3                                    deflocculant                                                                  pH               8.6     8.4     8.3   8.4                                    Rheology after hot rolling at 150° F. for 16 hours                     PV, cPs          4.5    12      18     17                                     YP,lb/100 ft.sup.2                                                                             3       8      15     27                                     I Gel, lb/100 ft2                                                                              2       6      10     4                                      10 Min Gel, lb/100 ft.sup.2                                                                    5      11      18     9                                      ______________________________________                                         *finished API barrel equivalent                                          

EXAMPLE II

Tests were performed and results were evaluated on the fresh water twocomponent modified liquid phase drilling fluid prepared as in Example Iin order to determine the lubricity characteristics of such a fluid.Lubricity coefficient testing was performed according to the APIspecifications set forth above. The results of this test clearly showthat the two component modified liquid phase drilling fluid of thepresent invention enables the drilling fluid to have increased lubricitycharacteristics as the concentration of polypropylene glycol mixture inthe fluid phase is increased. Results of this test are set forth, below:

                  TABLE 2                                                         ______________________________________                                        Polypropylene Glycol                                                          Mixture Concentration                                                                         Lubricity Coefficient                                         ______________________________________                                         0%             0.45                                                          10%             0.29                                                          20%             0.14                                                          40%             0.08                                                          ______________________________________                                    

EXAMPLE III

Tests were performed and results were evaluated in order to determineshale stabilization properties of the drilling fluid as prepared inExample I. A "shale" sample was prepared to simulate drilled cuttingsand was placed into the two component modified liquid phase drillingfluid and hot rolled at 150° F. for approximately 3 hours. Thereafter,the samples were removed from the hot roll oven, allowed to cool, andthe drilling fluid extracted. The amount of shale which was retained ona 30 mesh screen was determined by weighing said air dried shale. Inthis test, the more shale that is retained on the screen, the moreeffective is the drilling fluid composition in stabilizing the shale andpreventing or abating its dispersion. For purposes of this test, wedgesof the simulated shale were cut from a two inch diameter disc which wasformed by pressing minus 10 mesh plus 20 mesh shale fragments at 7600psi for 24 hours. In the table below, the percent retained on plus 30mesh screen after hot rolling for 3 hours at 150° F. is shown. In thistest, the results clearly indicate that the two component modifiedliquid phase drilling fluid of the present invention providessatisfactory shale stabilization and such shale stabilization propertiesare enhanced with increasing amounts of neutralized TPGB added in thepreparation of the drilling fluid.

                  TABLE 3                                                         ______________________________________                                                       Wt. % Shale Retained                                           % (Volume) TPGB                                                                              on 30 mesh screen                                              ______________________________________                                         0              4.3                                                           10             18.8                                                           20             10.0                                                           40             50.4                                                           ______________________________________                                    

EXAMPLE IV

Tests were performed and results were evaluated in order to determinethe thermal stability of the properties of the two component modifiedliquid phase drilling fluid of the present invention. In this test, thepolypropylene glycol mixture was TPGB and was added in an amount of 30%by volume of liquid phase. The water phase of the drilling fluid was 70%Houston, Tex. tap water. The drilling fluid also contained in an amountof pounds per barrel the following: (1) 10 ppb prehydrated bentonite;(2) 10 ppb formaldehyde-treated lignin/lignite filtration controladditive; (3) 0.4 ppb lignosulfonate deflocculant; and (4) 100 ppbbarite (weighting agent). Flow properties were determined before andafter hot rolling the fluid at 300° F. for 16 hours. The rheologicalproperties were measured at 120° F. As shown in Table 4, the propertiesof such a laboratory-prepared drilling fluid composition of the presentinvention exhibited satisfactory flow properties, after aging at atemperature of 300° F.

                  TABLE 4                                                         ______________________________________                                        Flow Properties of Two-Component Modified Liquid                              Phase Drilling Fluid                                                          600   300    200    100  6   3   1G   10G  pH   PV/YP                         ______________________________________                                        Fann 35 Rheology, 120° F.                                              Initial                                                                       100   55     39     23   4   3   4    45   10.2 45/10                         After hot rolling at 300° F.                                            84   50     38     25   9   9   9    44    8.0 34/16                         ______________________________________                                    

EXAMPLE V

The laboratory sample of Example IV was utilized to demonstrate thefiltration control effectiveness of the fluid. The filtration rates weredetermined on the aged fluid using standard API procedures with aresultant filtrate loss of only 5.2 cm³ in 30 minutes. A hightemperature, high pressure filtration rate was measured while exposingthe sample to a temperature of 300° F. and at a differential pressure of500 psi. The resultant filtrate loss of such test was found to be 15 cm³in 30 minutes.

EXAMPLE VI

The aged drilling fluid sample of Example IV was tested for lubricitycharacteristics, and was found to have a lubricity coefficient of 0.18,indicating that a weighted drilling fluid of the present invention whichalso contained a filtration control additive and barite still providedexcellent lubricity characteristics.

EXAMPLE VII

The aged fluid of Example IV also was tested for shale stabilizationcharacteristics. Eighty-one percent (81%) by weight of the shaleparticulate wedge prepared and tested as described in Example III wasretained on a 30 mesh screen after hot rolling at 150° F. for threehours. Thus, this weighted, two component modified liquid phase drillingfluid has been found to exhibit satisfactory shale stabilizationproperties when weighted with conventional weighting agents, such asbarite.

EXAMPLE VIII

Tests were performed and results were evaluated on a laboratory preparedtwo component modified liquid phase drilling fluid of the presentinvention incorporating sea water as the aqueous phase. A naturallyoccurring mineral viscosifier, sepiolite, was incorporated into adrilling fluid sample utilizing 30% by volume TPGB and 70% by volume seawater to form the aqueous phase. The sepiolite was added in an amount of12 ppb, rheological properties and lubricity characteristics weremeasured utilizing the testing procedures described in earlier examples,above, indicating that the drilling fluid so prepared exhibitedsatisfactory fluid flow properties; and provided lubricity to thesystem. The results are set forth in the table below:

                  TABLE 8                                                         ______________________________________                                        Properties of Two-Component Modified Liquid Phase Drilling                    Fluids                                                                        ______________________________________                                        A. Flow Properties after hot rolling at 150° F., 16 hours              Fann 35 Rheology, Room Temperature                                            %                                                  PV/                        TPGB  600    300    200  100  6   3   1G  10G  pH  YP                         ______________________________________                                         0    24     21     20   18   12  11  12  18   7.5 3/18                       30    23     16     13   10    5   5   6   7   9.1 7/9                        ______________________________________                                        B. Lubiicity Coefficient                                                      % TPGB      Lubricity Coefficient                                             ______________________________________                                         0          .46                                                               30          .24                                                               ______________________________________                                    

EXAMPLE IX

Tests were performed and results were evaluated on an additional twocomponent modified liquid phase drilling fluid incorporating seawaterinto the fluid phase. The drilling fluid was similar to that preparedand tested in Example VIII. In this test, a sample was prepared whichcontained the same ratio of polypropylene glycol mixture/seawater andsepiolite, as in Example VIII but varied with respect to the addition ofa lignosulfonate deflocculant, barite, and a filtration controladditive. In this test, MIL-PAC LV was utilized as a filtration controlagent, and is a cellulose derivative. The composition, flow properties,lubricity characteristics and shale stabilization results are set forthin the following table:

                  TABLE 9                                                         ______________________________________                                        PROPERTIES OF SIMULATED DRILLING FLUID                                        CONTAINING 30% TPGB - 70% SEAWATER AS THE                                     LIQUID PHASE                                                                  ______________________________________                                        Composition, lb/bbl                                                           ______________________________________                                        Sepiolite         10                                                          MIL-PAC LV        2                                                           MIL-REZ           10                                                          UNI-CAL           1                                                           Barite            300                                                         Weight, lb/gal    13.9                                                        ______________________________________                                        A. Flow Properties                                                            Fann 35 Rheology, 120° F.                                              600   300    200    100  6   3   1G   10G  pH   PV/YP                         ______________________________________                                        Initial                                                                       47    26     20     14   9   9   17   36   9.0  21/5                          After hot rolling at 300° F., 16 hours                                 46    24     18     13   7   7   11   19   8.6  22/2                                                HTHP                                                    Filtrates, cc  API    (300° F., 500 psi)                                              10.2   16.8                                                    ______________________________________                                        B. Lubricity Coefficient: .09                                                 C. Shale Stabilization: Wt. % retained on 30 mesh screen                      ______________________________________                                        >95%                                                                      

EXAMPLE X

Tests were run and rseults were evaluated to determine the ability ofvarious test fluids to inhibit swelling of sodium bentonite samples.Listed below are the test fluids used in the swelling tests:

    ______________________________________                                        SAMPLE         ADDITIVE                                                       ______________________________________                                        A,B,C          Deionized water (blank)                                        D              Propylene glycol (100%)                                        E              Tripropylene glycol (100%)                                     F              Diesel Oil (100%)                                              G              TPG bottoms (50%)                                              H,I            Glycerin (50%)                                                 J,K            Glycerin (25%)                                                 L,M,N          Propylene glycol (50%)                                         O,P,Q          Sorbitol (50%)                                                 R              Alcohol initiated EO-PO                                                       copolymer* (50%)                                               S              EO-PO copolymer** (50%)                                        ______________________________________                                         *Poly-tergent S305 LF  Olin Chemical Corporation                              **Polyglycol 15-200  Dow Chemical Company                                

In the tests where more than one sample was prepared and tested (i.e.,A,B,C; H,I; J,K; L,M,N; O,P,Q) linear swelling calculations wereaveraged to reflect the percentage increase in swelling, initially, andover a period of time, in comparison to the blank.

In order to determine the swelling characteristics of the fluid to theswelling inhibition characteristics of a hydrocarbon, diesel oil wastested for swelling characteristics, SAMPLE F.

For each test, a pellet was prepared by compacting approximately 5 gramsof sodium bentonite with a moisture content of from between about 28 toabout 32 percent by weight in a 0.5 in. diameter die under approximately2500 lbs load (12,500 psi) for approximately 6 minutes. The length ofeach pellet was measured by micrometer, and each pellet was weighed. Thedensity of the pellets varied from 1.78 to 1.82 g/cm³. Thereafter, eachpellet was placed in a 3×5 inch plastic bag, and positioned in adigimatic swellmeter, which was utilized to determine swelling of aparticulate sample. Thirty (30) ml of the fluid (or diesel, or blank)which was tested was placed in the bag. The amount of linear swellingwas recorded versus time.

In addition to observing swelling rates of the samples in the variousfluids in these tests, the condition of the bentonite pellet was alsomeasured perpendicular to the length of the pellet cylinder with apenetrometer needle weighing 0.616 pounds and having a surface area of1.20×10⁻³ square inches. This combination of weight and surface areaproduced a force of 510 pounds per square inch at the surface of theparticulate pellet. This penetration depth gives a measure of therelative hardness of the pellets.

In these tests on sodium bentonite pellets, a penetrometer reading of 12or greater indicated that the pellet had lost practically all of itsintegrity; a penetrometer reading of 2 or less indicates that verylittle bentonite hydration occurred over the test period.

The results of this test are set forth in the table below:

                  TABLE 10                                                        ______________________________________                                        LINEAR SWELLING OF SODIUM BENTONITE                                           IN DEIONIZED WATER                                                                      Percent Linear Swelling                                             Time (min.) A      B          C    Ave %                                      ______________________________________                                         5          0.22   0.16       0.22 0.20                                       10          0.50   0.46       0.99 0.48                                       15          0.77   0.76       0.77 0.77                                       30          1.41   1.59       1.61 1.54                                       60          2.38   2.62       2.89 2.63                                       120         3.58   3.37       4.11 3.69                                       ______________________________________                                    

                  TABLE 10A                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS                                         OF SODIUM BENTONITE IN VARIOUS FLUIDS                                                  Percent Linear Swe11ing                                              Time (min.)                                                                              D       E          F     G                                         ______________________________________                                         5         -0.13   -0.19      -0.02 0                                         10         -0.17   -0.23      -0.04 -0.01                                     15         -0.19   -0.26      -0.04 -0.01                                     30         -0.28   -0.36      --    -0.01                                     60         -0.35   -0.58      -0.04 -0.02                                     120        --      --         --    -0.14                                     Hardness   --      --         1.5   0                                         (mm)                                                                          ______________________________________                                    

                  TABLE 10B                                                       ______________________________________                                        LINEAR SWELLING OF SODIUM BENTONITE                                           IN 50% (W/W) GLYCERIN                                                                  Percent Linear Swelling                                              Time (min.)                                                                              H            I      Ave %                                          ______________________________________                                         5         0.12         0.06   0.09                                           10         0.21         0.16   0.18                                           15         0.27         0.23   0.25                                           30         0.48         0.42   0.45                                           60         0.82         0.69   0.76                                           120        1.32         1.23   1.28                                           ______________________________________                                    

                  TABLE 10C                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS                                         OF SODIUM BENTONITE IN 25% (W/W) GLYCERIN                                                Percent Linear Swelling                                            Time (min.)  J           K      Ave %                                         ______________________________________                                         5           0.12        0.26   0.19                                          10           0.35        0.55   0.45                                          15           0.55        0.76   0.66                                          30           1.1         1.29   1.20                                          60           1.94        2.01   1.98                                          120          3.02        2.90   2.96                                          Hardness (mm)                                                                              7.9         12.3                                                 ______________________________________                                    

                  TABLE 10D                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS                                         OF SODIUM BENTONITE IN 50% (w/w) PROPYLENE                                    GLYCOL                                                                                   Percent Linear Swelling                                            Time (min.)  L      M          N    Ave %                                     ______________________________________                                         5           0.05   0.07       0.05 0.06                                      10           0.12   0.17       0.10 0.13                                      15           0.17   0.24       0.16 0.19                                      30           0.33   0.51       0.35 0.40                                      60           0.68   1.1        0.78 0.85                                      120          1.43   1.95       1.44 1.61                                      Hardness (mm)                                                                              3.5    3.0        2.8                                            ______________________________________                                    

                  TABLE 10E                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS OF                                      SODIUM BENTONITE IN 50% (w/w) SORBITOL                                                   Percent Linear Swelling                                            Time (min.)  0      P          Q    Ave %                                     ______________________________________                                         5           0.06   0.07       0.05 0.06                                      10           0.11   0.13       0.11 0.12                                      15           0.17   0.19       0.16 0.17                                      30           0.32   --         0.28 0.30                                      60           0.64   --         0.46 0.55                                      120          1.1    --         0.83 0.96                                      15 HR        --     3.09       --   --                                        Hardness (mm)                                                                              3.0    10.0       3.0                                            ______________________________________                                    

                  TABLE 10F                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS OF SO-                                  DIUM BENTONITE IN 50% (w/w) POLY-TERGENT                                      S-305 LF                                                                                    Percent Linear Swelling                                         Time (min.)   R                                                               ______________________________________                                        10            0.22                                                            20            0.35                                                            30            0.44                                                            40            0.57                                                            50            0.65                                                            60            0.73                                                            90            0.94                                                            120           1.12                                                            Hardness (mm) 2.5                                                             ______________________________________                                    

                  TABLE 10G                                                       ______________________________________                                        LINEAR SWELLING AND RELATIVE HARDNESS OF SO-                                  DIUM BENTONITE IN 50% (w/w) POLYGLYCOL 15-200                                               Percent Linear Swelling                                         Time (min.)   S                                                               ______________________________________                                        10            0.24                                                            20            0.32                                                            30            0.38                                                            40            0.42                                                            50            0.45                                                            60            0.48                                                            90            0.52                                                            120           0.54                                                            Hardness (mm) less than 0.5                                                   ______________________________________                                    

EXAMPLE XI

The shale inhibition characteristics of the two component modifiedliquid phase drilling fluid of this invention (Mud A) were compared tothose of an oil-base fluid (Mud B). Composition of the two fluids aregiven below:

    ______________________________________                                                                  lb/bbl                                              ______________________________________                                        Mud A             Water         164.4                                         (Two component modified                                                                         MILGEL ®  5                                             liquid phase)     (gelling agent)                                                               Tripropylene  164.4                                                           glycol bottoms                                                                MILBAR ® (barite)                                                                       90                                                              UNI-CAL ® 0.5                                                             (deflocculant)                                              Mud B             Oil (Low Viscosity                                                                          147.8                                         (Oil Mud)         Mineral Seal)                                                                 30% CaCl.sub.2                                                                              124.5                                                           solution                                                                      Barite        123                                                             CARBO-MUL ®                                                                             1.9                                                             (invert emulsifier)                                                           CARBO-GEL ®                                                                             4.0                                                             (gelling agent)                                             ______________________________________                                    

The flow characteristics at 120° F. of these two fluids after hotrolling at 150° F. for 16 hours are shown in Table 11A.

                  TABLE 11A                                                       ______________________________________                                                         Mud A Mud B                                                  ______________________________________                                        PV,cPs             13      15                                                 YP, lb/100 ft2      9      7                                                  I Gel, lb/100 ft.sup.2                                                                            9      7                                                  10 Min. Gel, lb/100 ft.sup.2                                                                     15      9                                                  ______________________________________                                    

The percent linear swelling of a sodium bentonite pellet exposed to thetwo component modified liquid phase drilling fluid and the oil baseddrilling fluid is shown in Table llB. The procedure used to measure thelinear swelling is described on pages 52-53, "Swelling Test" of paperentitled "Rigsite Shale Evaluation Techniques for control ofShale-related Wellbore Instability Problems", SPE/IADC Paper 16054(1987).

                  TABLE 11B                                                       ______________________________________                                                   Percent Linear Swelling in 60 Minutes                              ______________________________________                                        Mud A        -0.44                                                            (2 component modified                                                         liquid phase)                                                                 Mud B        -0.23                                                            (oil-based)                                                                   ______________________________________                                    

As shown by the data, both fluids caused the sodium bentonite pellet tocontract (decrease in length) indicating that moisture had beenwithdrawn from the pellet. In this case, dehydration of the two pelletsoccurred, which is characteristic of oil base fluids whose osmoticactivity is controlled by the concentration of calcium chloride salt inthe internal water phase.

The relative hardness of the sodium bentonite pellets at the end of thelinear swelling test was determined using the penetrometer to measurethe depth of penetration of a needle into the pellet. The results aregiven in Table llC below:

                  TABLE 11C                                                       ______________________________________                                                          Depth of Penetration, mm                                    ______________________________________                                        Mud A               0                                                         (Two component modified liquid                                                phase)                                                                        Mud B               0.5                                                       (oil-based)                                                                   ______________________________________                                    

This data shows that the two component modified liquid phase drillingfluid preserves the integrity of the sodium bentonite pellet as does theoil base fluid.

The comparison shows that the two-component modified liquid phasedrilling fluid is capable of stabilizing shale in a manner similar tothat of an oil-based fluid.

EXAMPLE XII

In another example, two typical state-of-the-art water based laboratorprepared muds were compared to the two component modified liquid phasedrilling fluid of this invention. Compositions of the three test fluidsare given below:

    ______________________________________                                                  lb/bbl                                                              ______________________________________                                        Mud A       Water               328.7                                         (Lignosulfonate)                                                                          MILGEL ®        22.8                                                      (gelling agent)                                                               UNI-CAL ®       2.5                                                       (deflocculant)                                                                MIL-BAR ®       90.0                                                      (barite weighting agent)                                                    NaOH pH to 9.5                                                      Mud         Water               328.7                                         (PHPA Polymer)                                                                            NEW-DRILL HP        1.0                                                       MILGEL ®        10                                                        NEW-THIN            0.2                                                       (deflocculant)                                                                MIL-BAR             90.0                                                    NaOH pH to 9.5                                                      Mud C       Water               230.1                                         (Two Component                                                                            MILGEL              8.5                                           Liquid Phase)                                                                             Tripropylene        98.6                                                      Glycol Bottoms                                                                MIL-BAR             90.0                                                      UNI-CAL ®       0.75                                                      XC Polymer          0.3                                                       (Xanthomonus campestris shear -                                               thinning synthetic polymer)                                       ______________________________________                                    

The flow properties of these fluids after hot rolling at 150° F. for 16hours are as follows:

                  TABLE 12A                                                       ______________________________________                                        FLOW PROPERTIES                                                               Fann 35 Rheology, 120° F.                                                                                                PV/                         600      300    200    100  6   3   1G  10G  pH   YP                          ______________________________________                                        Mud A 56     32     22   13   3   2.5 3   4    9.4  24/8                      Mud B 24     16     12    9   5   5   8   21   9.4   8/8                      Mud C 40     23     16   10   3   2.5 4   9    11.3 17/6                      ______________________________________                                    

The percent linear swelling of a reconstituted "gumbo" shale testspeciment determined as by procedure described on pages 52-53, "SwellingTest" of paper entitled "Rigsite Shale Evaluation Techniques for Controlof Shale-related Wellbore Instability Problems", SPE/IADC Paper No.16054 (1987 for the three drilling fluids is as follows:

                  TABLE 12B                                                       ______________________________________                                                % Linear Swelling in 60 minutes                                       ______________________________________                                        Mud A     5.0 (Avg.)                                                          Mud B     5.1 (Avg.)                                                          Mud C     3.8 (Avg.)                                                          ______________________________________                                    

Using the penetrometer, the hardness (or lack thereof) of the testspecimens after the Swelling Test was determined. The depth ofpenetration of the needle into the speciment is an indication of thedegree of hardness or softness of the specimen upon completion of thetest. The lower the value, the more inhibitive the test fluid. In thisexample, the two component modified liquid phase system of saidinvention was appreciable more inhibitive.

                  TABLE 12C                                                       ______________________________________                                        Relative Hardness                                                                      Penetration depth, mm                                                ______________________________________                                        Mud A      6.0                                                                Mud B      6.0                                                                Mud C      1.0                                                                ______________________________________                                    

The lubricity coeffcient of the three muds were determined by the methodpreviosuly described and is shown in Table 12D below:

                  TABLE 12D                                                       ______________________________________                                                 Lubricity Coefficient                                                ______________________________________                                        Mud A      .33                                                                Mud B      .31                                                                Mud C      .20                                                                ______________________________________                                    

The data of this example show that a two component modified liquid phasedrilling fluid (Mud C) exhibits flow properties similar to those of alignosulfonate drilling fluid and a polymer drilling fluid and issuperior as a shale inhibiting fluid and shows improved lubricity.

EXAMPLE XIII

The 96 hr. LC₅₀ ¹ for Mysidopsis Almyna of an 80:20 oil based drillingfluid in which a Mineral Seal Oil, Mentor-28, (Exxon Company) was usedas the oil phase was found to be 50,000 ppm (5%) in the suspendedparticulate phase. The 96 hr LC₅₀ for Mysidopsis bahia on alaboratory-prepared lignosulfonate mud (Generic Mud No. 7) containing17% tripropylene glycol bottoms was 160,000 ppm (16%) in the suspendedparticulate phase showing that the fluid of said invention is less toxicto mysid shrimp than oil base fluid.

Although the invention has been described in terms of specifiedembodiments which are set forth in detail, it should be understood thatthis is by illustration only and that the invention is not necessarilylimited thereto, since alternative embodiments and operating techniqueswill become apparent to those skilled in the art in view of thedisclosure. Accordingly, modifications are contemplated which can bemade without departing from the spirit of the described invention.

What is claimed and desired to be secured by Letters Patent is:
 1. Amethod of inhibiting the swelling of shale in a modifed non-pollutingliquid phase drilling fluid, comprising the steps of:(1) preparing anon-polluting modified liquid phase drilling fluid consistingessentially of (a) a water phase consisting of fresh water, seawater,brine, simulated brine, or mixtures thereof; (b) a water-solublecomponent which is tripropylene glycol bottoms having from between about5% and about 20% by volume tripropylene glycol and from between about95% and about 80%, by volume, polypropylene glycol highers, the ratio ofsaid water-soluble component to the total liquid phase being frombetween about 5% to about 50% by volume; (c) a viscosifier forsuspension of solids in said liquid phase; and (d) a filtration controlagent, the linear swelling on a reconstituted "gumbo" shale inserted insaid drilling fluid for about 60 minutes being lower than that forsubstantially the same fluid without the water soluble component, asmeasured by the "Swelling Test", Rigsite Shale EValuation Techniques forControl of Shale-Related Wellbore Instability Problems, SPE/IADC PaperNO. 16054, pp. 52-53 (1987), said drilling fluid being less toxic tomysid shirimp than an 80:20 oil based drilling fluid containing amineral seal oil as the oil phase following toxicity test procedures asset forth in "Acute Toxicity of Eight Laboratory Prepared GenericDrilling Fluids to Mysids (Mysidopsss Bahia)", 1984 EPA-600/3-84-067;and (2) circulating said drilling fluid into, through and out of saidsubterranean well whereby said drilling fluid contacts formationparticulate matter and the bore of said well to thereby inhibit theswelling of the shale.